Here's something I just figured out today. Seems obvious now that I realize it, but had never thought of it before:
I'm firing my little 1 cubic foot manual test kiln with some fusion buttons for my glaze formulation students. I just recently hooked it up an external Orton digital controller I got from a customer. For those of you who haven't used one, the way external controllers work is the kiln plugs into the controller unit via its regular power cord, and the controller sends power through the cord as needed to heat up the kiln. It cycles the kiln on and off like any digital controller, to control the rate of climb.
The kiln itself has a Sitter on it with a timer. You have to put a cone in the sitter that's higher than the projected firing (or just jam a piece of kiln shelf in it), push the power button, and turn all the knobs on high. Because power is only going through the sitter intermittently, as the relays in the digital control unit cycle the power on and off, the timer on the sitter only moves when there is power to the kiln. So at the end of a firing I can tell exactly how long the kiln was 'on', and calculate the cost of the firing by way of the wattage of the kiln. Awesome!